The present invention relates broadly to a casing member for a WDM add/drop multiplexer unit, to a chassis member for carrying at least one circuit board, and to a WDM multiplexer module. The present invention also relates to an optical network node and to an optical network.
Optical networks may be classified into long haul optical networks, metro optical networks, access optical networks and enterprise gear-optical networks. Distinctions between the different types may in a fist instance be drawn on the basis of physical transmission distances covered, decreasing from long haul optical networks down to enterprise gear-optical networks, with the latter being typically implemented within one location e.g. in one office building.
The different types of optical networks can also be distinguished in terms of the physical environment in which in particular add/drop equipment is located. For example, for enterprise gear-optical networks, the add/drop equipment is typically located inside of air conditioned buildings, and therefore no particular extreme temperature condition compliance is required to implement such optical networks. For long haul and metro optical networks, which typically involve very complex and expensive equipment, add/drop equipment is typically located in telecommunications carriers central offices and points of presence and are subjected to a limited range of temperatures, which is sometimes referred to as requiring the add/drop equipment to be carrier class compliant This temperature range is typically in the range of xe2x88x925 to 55xc2x0 C. as required for Telcordia NEBS level 3.
However, in access optical networks the add/drop equipment is typically located in an outside plant (OSP) situation, and thus potentially subjected to a wider temperature range than e.g. carrier class compliance requirements.
Currently, the only optical networks that can be implemented in scenarios where the required add/drop equipment is located in an OSP situation are Time Domain Multiplexing (TDM) based networks. So far, WDM based optical networks have not been deemed suitable for implementation in OSP situations, as currently available WDM equipment is not OSP compatible. However, it would be desirable to implement WDM based optical networks in such an environment, to utilise the larger capacity in the optical domain in access optical networks.
At least preferred embodiments of the present invention seek to provide a casing member for a WDM add/drop multiplexer module, a chassis member for carrying at least one circuit board, or a WDM multiplexer module suitable for use in an OSP situation.
In accordance with a first aspect of the present invention there is provided a casing member for a WDM add/drop multiplexer unit, the casing member comprising a backplane for interconnection of components of the WDM add/drop multiplexer unit inserted in the casing member, and at least one heat sink opening formed in a wall of the casing member disposed to, in use, receive a heat sink structure of a component of the WDM add/drop multiplexer unit in a manner such that the heat sink structure is exposed to an ambient around the casing member when the component is mounted in the casing member, for facilitating maintaining a controlled temperature environment inside of the component.
Preferably, the heat sink opening is formed in the backwall incorporating the backplane.
A pair of heat sink openings may be formed in a mirrored configuration on either side of the backplane with respect to a centreplane halfway along the width of the casing member.
In one embodiment, the casing member further comprises a first key member arranged, in use, to prevent a component of the WDM add/drop multiplexer unit from contacting the backplane, when said component is inserted upside down in its intended slot, or when it is inserted in another component""s intended slot, and wherein the first key member is adapted to cooperate with a heat sink structure of said component.
The casing member may further comprise a second key member arranged, in use, to prevent a component of the WDM add/drop multiplexer unit from contacting the backplane, when said component is inserted upside down in another component""s intended slot, and wherein the second key member is adapted to co-operate with a third key member formed on said component.
The casing member may further comprise at least one vent opening in one wall of the casing member. Preferably, the casing member comprises at least one pair of vent openings, the openings of the pair being formed in opposite walls of the casing member. In one embodiment, the at least one pair of vent openings is formed in the sidewalls of the housing. Alternatively or additionally, at least one pair of vent openings is formed in the top and bottom walls of the housing element.
The housing element may be adapted for horizontal or vertical mounting.
In a preferred embodiment, the housing element is adapted for mounting onto a rack structure.
In one embodiment, the casing member further comprises a heat sink unit mounted onto the casing member and adapted, in use, when components of the WDM add/drop multiplexer unit are inserted in the casing member, to make thermal contact with at least one of the components, for facilitating maintaining a controlled temperature environment inside of said component. Preferably, the heat sink unit is arranged in a manner such that, in use, the interconnection to said component is releasable.
The heat sink unit may be incorporated in the backwall incorporating the backplane. The heat sink unit may be formed on the backplane.
Preferably, the heat sink unit comprises a plurality of substantially planar fins disposed substantially parallel to the backwall of the casing member, and mounted by way of at least one longitudinal mounting member expanding substantially perpendicularly from the backwall. Accordingly, convection airflow between the fins is preferably not inhibited in either a horizontal or a vertical mounting position of the casing member.
The casing element may optionally further comprise at least one fan device mounted on the outside of the housing element and disposed in a manner such that, in use when the heat sink structure of the component of the WDM add/drop multiplexer unit extends through the heat sink opening of the housing element, the heat sink structure is subjected to an airflow generated by the fan device.
The casing member may further comprise at least one baffle structure externally mounted or formed on the casing member, and arranged in a manner such that in use when the casing member is mounted vertically into the rack structure, convection airflow from one heat sink structure or heat sink unit is diverted away from other heat sink structures or heat sink units.
In accordance with a second aspect of the present invention, there is provided a chassis member for carrying at least one circuit board, wherein the chassis member is adapted, in use, to function as a heatsink for a heat generating component mounted on the circuit board.
Preferably, a main body of the chassis is contoured or shaped in a manner such that, in use, a distance between the heat generating component and a region of the main body facing the heat generating component is reduced compared to other components on the circuit board.
Advantageously, the chassis member comprises sidewalls formed around the peripheral region of the main body and adapted to function in use, as at least a portion of housing sidewalls of a housing structure for the circuit board.
In one embodiment, the chassis member is adapted, in use, to carry at least one circuit board above and at least one circuit board below of the main body.
In accordance with a third aspect of the present invention, there is provided a WDM multiplexer module comprising a housing, a chassis member located substantially inside the homing and adapted to function as a heat sin, a heat sink structure extending from the housing and in thermal communication with the chassis member, at first thermoelectric (TE) device in thermal communication with the chassis member, at least one heat generating electrical component in thermal communication with the chassis member, and a control unit arranged, in use, to maintain a controlled temperature environment inside the housing utilising the heat sink structure, the TE device, and the heat generating electrical component and utilising the chassis member as a thermal communication medium.
Preferably, the module further comprises a local thermal environment structure located inside the housing and a second TE device in thermal communication with the chassis member and the local thermal environment structure, whereby, in use, a second stage controlled temperature environment is created substantially inside the local thermal environment structure, and wherein temperature variations in the second stage controlled temperature environment are smaller than temperature variations inside the housing.
In one embodiment, the module comprises at least one laser source disposed in a manner such that, in use, the source temperature of the laser source is substantially governed by the second stage controlled temperature environment. Preferably, the laser source is a semiconductor laser source, and a junction of the laser source is located substantially inside the local thermal environment structure.
The module may comprise a plurality of electrical components, and the control unit may further be arranged, in use dung start-up or re-start of the module, to sequentially switch on the electrical components based on operating temperature specifications and heat generating characteristics of the electrical components to facilitate creation of the controlled temperature environment.
Advantageously, the heat sink structure comprises at least one heat pipe. In one embodiment, the heat pipe has a working fluid characterized by a freezing temperature above xe2x88x9240xc2x0 C., whereby a discontinuity in heat transfer to and from the heat sink structure is created for temperatures below the freezing temperature of the working fluid in the heat pipe for reducing heat loss from the inside of the housing. In one preferred embodiment, the freezing temperature is about zero xc2x0 C.
Advantageously, the chassis member comprises side walls formed around the peripheral region of a main body of the chassis member, and said side walls form at least a portion of housing side walls of the housing.
In a preferred embodiment, the housing is adapted to function as an electro-magnetic induction (EMI) shield.
The module may Anther comprise a first key member arranged, in use, to cooperate with a second key member formed on a casing member into which the module is inserted, to prevent the module from making contact with a backplane of the casing member when the module is inserted upside down into a slot of the casing member for which the module is not intended.
In accordance with a fourth aspect of the present invention, there is provided a method of thermal control of a WDM multiplexer module, the method comprising the steps of maintaining a first stage controlled temperature environment inside the module and maintaining a second stage controlled temperature environment in at least a portion of the inside of the module, wherein temperature variations in the second stage controlled temperature environment are smaller than temperature variations of the first stage controlled temperature environment.
In one embodiment, the module comprises at least one laser source, and the source temperature of the laser source is substantially governed by the second stage controlled temperature environment.
The module may comprise a plurality of electrical components, and the method may further comprise, during start-up or re-start of the module, the step of sequentially switching on the electrical components based on operating temperature specifications and heat generating characteristics of the electrical components to facilitate creation of the first stage controlled temperature environment.
Advantageously, the maintaining of the first and second stage controlled temperature environments comprises utilising at least one heat pipe. In one embodiment, the heat pipe has a working fluid characterised by a freezing temperature above xe2x88x9240xc2x0 C., whereby a discontinuity in heat transfer to and from the heat sink structure is created for temperatures below the freezing temperature of the working fluid in the heat pipe for reducing heat loss from the inside of the housing. In one preferred embodiment, the freezing temperature is about zero xc2x0 C.
In accordance with a fifth aspect of the present invention, there is provided an optical network node incorporating a casing member for a WDM add/drop multiplexer unit in accordance with the first aspect of the present invention, a chassis member for carrying at least one circuit board in accordance with the second aspect of the present invention, or a WDM multiplexer module in accordance with the third aspect of the present invention.
In accordance with a sixth aspect of the present invention, there is provided an optical network incorporating an optical network node in accordance with the fifth aspect of the present invention.